Drupal a free and open-source content-management framework written in PHP and distributed under the GNU General Public License, provides a back-end framework for at least 2.2% of all Web sites worldwide – ranging from personal blogs to corporate, political, and government sites. Systems also use Drupal for knowledge management and for business collaboration.
The standard release of Drupal, known as Drupal core, contains basic features common to content-management systems. These include user account registration and maintenance, menu management, RSS feeds, taxonomy, page layout customization, and system administration. The Drupal core installation can serve as a simple Web site, a single- or multi-user blog, an Internet forum, or a community Web site providing for user-generated content.
"The Drupal Overview", a feature of the project web site, describes it as a content management framework. Drupal also describes itself as a Web application framework, as it meets the generally accepted[by whom?] feature requirements for such frameworks.
Although Drupal offers a sophisticated API for developers, basic Web-site installation and administration of the framework require no programming skills.Drupal runs on any computing platform that supports both a Web server capable of running PHP and a database to store content and configuration.
Drupal can automatically notify the administrator about new versions of modules, themes, or the Drupal core. It's important to update quickly after security updates are released. Before updating it is highly recommended to take backup of core, modules, theme, files and database. If there is any error shown after update or new updates is not compatible with a module, then it can be quickly replace by backup. There are several backup modules available in Drupal. On October 15, 2014, a sql injection vulnerability was announced and update released. Two weeks later the Drupal security team released an advisory explaining that everyone should act under the assumption that any site not updated within 7 hours of the announcement are infected. Thus, it can be extremely important to apply these updates quickly and usage of a tool to make this process easier like drush is highly recommended.
Prior to version 7, Drupal had functions that performed tasks related to databases, such as SQL query cleansing, multi-site table name prefixing, and generating proper SQL queries. In particular, Drupal 6 introduced an abstraction layer that allowed programmers to create SQL queries without writing SQL.
Drupal 7 extends the data abstraction layer so that a programmer no longer needs to write SQL queries as text strings. It uses PHP Data Objects to abstract the database. Microsoft has written a database driver for their SQL Server. Drupal 7 supports the file-based SQLite database engine, which is part of the standard PHP distribution.
With Drupal 7's new database abstraction layer and ability to run on the Windows web server IIS, it is now easier for Windows developers to participate in the Drupal community. A group on Drupal.org is dedicated to Windows issues.
With the release of Drupal 7, Web accessibility has been greatly improved by the Drupal community. Drupal is a good framework for building sites accessible to people with disabilities, because many of the best practices have been incorporated into the program code Core. The accessibility team is carrying on the work of identifying and resolving accessibility barriers and raising awareness within the community. Drupal 7 started the adoption of WAI-ARIA support for Rich Internet Applications and this has been carried further in Drupal 8. There have been many improvements to both the visitor and administrator sides of Drupal, especially:
Drag and drop functionality
Improved color contrast and intensity
Adding skip navigation to Core themes
Adding labels by default for input forms
Fixing CSS display:none with consistent methods for hiding and exposing text onfocus.
The community also added an accessibility gate for Core issues in Drupal 8.
As of February 2015, there are more than 2,000 free community-contributed themes. Themes adapt or replace a Drupal site's default look and feel.
Drupal themes use standardized formats that may be generated by common third-party theme design engines. Many are written in the PHPTemplate engine or, to a lesser extent, the XTemplate engine. Some templates use hard-coded PHP. Drupal 8 will integrate the Twig templating engine.
The inclusion of the PHPTemplate and XTemplate engines in Drupal addressed user concerns about flexibility and complexity. The Drupal theming system utilizes a template engine to further separate HTML/CSS from PHP. A popular Drupal contributed module called 'Devel' provides GUI information to developers and themers about the page build.
Community-contributed themes at the Drupal website are released under a free GPL license, and most of them are demonstrated at the Drupal Theme Garden.
In the past, those wanting a fully customized installation of Drupal had to download a pre-tailored version separately from the official Drupal core. Today, however, a distribution defines a packaged version of Drupal that upon installation, provides a website or application built for a specific purpose.
The distributions offer the benefit of a new Drupal site without having to manually seek out and install third-party contributed modules or adjust configuration settings. They are collections of modules, themes, and associated configuration settings that prepare Drupal for custom operation. For example, a distribution could configure Drupal as a "brochureware" site rather than a "news" site or an "online store"
Drupal is based on the Presentation Abstraction Control architecture, or PAC. The menu system acts as the Controller. It accepts input via a single source (HTTP GET and POST), routes requests to the appropriate helper functions, pulls data out of the Abstraction (nodes and, from Drupal 5 onwards, forms), and then pushes it through a filter to get a Presentation of it (the theme system). It even has multiple, parallel PAC agents in the form of blocks that push data out to a common canvas (page.tpl.php).
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